1. Field of the Invention
The present invention relates to a double-chuck mechanical pencil provided with a front chuck for gripping a lead, and a back chuck provided with a chuck ring loosely put thereon to project a lead by a fixed length and, more particularly, to a double-chuck mechanical pencil provided with an eraser support structure in its back portion.
2. Prior Art
There have been proposed various double-chuck mechanical pencils incorporating improvements to reduce waste leads. In the double-chuck mechanical pencil of this kind, if either the front or the back chuck is turned by some cause while a lead is gripped by both the front and the back chuck, the lead is twisted and broken. Fragments of the broken lead remaining in a space between the front and the back chuck obstruct a lead projecting operation, and a front portion and a back portion of the broken lead are dislocated relative to each other in projecting the broken lead to make the projection of the broken lead impossible.
If the user turns a push cap or an eraser holder connected through a lead tank to the back chuck inadvertently or the back chuck is turned together with the lead tank when an eraser is used, a lead gripped by both the front and the back chuck is twisted and broken.
Accordingly, it is an object of the present invention to provide a double-chuck mechanical pencil with an eraser, having a barrel, a lead tank, an adapter combined with the barrel and the lead tank so that chucks are able to slide axially and unable to rotate, and restraining means provided on the adapter and a rubber eraser support member to prevent the torsional breakage of a lead.
A mechanical pencil of this kind has complicated internal mechanisms and a sufficient space for containing an eraser cannot be secured in a back portion of the barrel of the mechanical pencil. Such a problem is more serious in a double-chuck mechanical pencil provided with a lead holding chuck and a lead advancing chuck to reduce waste leads.
Pencil marks drawn on a paper sheet with the mechanical pencil can be rubbed out with an eraser, because scraps of rubber are produced when the surface of the paper sheet is rubbed with the eraser, and the scraps of rubber adsorb and envelop carbon particles forming the pencil marks. Therefore, the eraser is abraded and worn out rapidly. The present invention has been made taking into consideration the complicated structure of double-chuck mechanical pencils and the characteristics of the eraser and it is an object of the present invention to enable an eraser projecting mechanism to be easily removed regardless of the change in shape of the eraser and to enable the eraser to be projected by an appropriate length when the same is abraded.
Another object of the present invention is to eliminate structural disadvantages of an eraser, to enable the use of either of a plastic eraser and a rubber eraser without trouble, to overcome difficulty in directly removing a worn or deteriorated eraser when replenishing the mechanical pencil with leads, and to provide an eraser support structure capable of being easily removed without making finger tips dirty with a dirty eraser.
A third object of the present invention is to enable an eraser to be put relatively easily on a back portion of a mechanical pencil regardless of the size and the shape thereof and manufacturing errors therein, to enable the mechanical pencil to be replenished easily and accurately with leads, to avoid torsionally breaking a lead chucked in a front lead chuck and a back lead chuck by the turning of the back lead chuck together with a lead tank turned by the eraser when the eraser is used.
A fourth object of the present invention is to prevent a lead from being held in a space between a barrel and a lead tank of a diameter different from that of the barrel, and the lead tank from rattling when an eraser is used by providing an adapter serving as a spacer between the barrel and the lead tank.
According to a first aspect of the present invention, there is provided a double-chuck mechanical pencil having a front lead chuck for holding a lead and a back lead chuck for advancing a lead, comprising: a barrel; a lead tank connected to the back lead chuck; an adapter fixedly put on a back portion of the lead tank, restrained from rotation relative to the barrel and axially movable; and a rotary eraser projecting mechanism provided with a support member restrained from rotation relative to the adapter, detachably connected to a back portion of the adapter.
According to a second aspect of the present invention, there is provided a double-chuck mechanical pencil having a front lead chuck for holding a lead and a back lead chuck for advancing a lead, said double-chuck mechanical pencil comprising: a barrel; a lead tank connected to the back lead chuck; an adapter fixedly put on a back portion of the lead tank, restrained from rotation relative to the barrel and axially movable; and an eraser support structure provided with a support member restrained from rotation relative to the adapter, and detachably connected to a back portion of the adapter.
According to a third aspect of the present invention, there is provided a double-chuck mechanical pencil having a front lead chuck for holding a lead and a back lead chuck for advancing a lead, comprising: a barrel provided with a detaining means on the inner circumference thereof, a lead tank connected to the back lead chuck; an adapter fixedly put on a back portion of the lead tank, having an expanded front portion receiving the lead tank therein and provided with a detaining means on the outer circumference thereof, restrained from rotation relative to the barrel and axially movable; and an eraser support member provided on a back portion of the adapter.